"It's parked just south of here," the guy with the laptop announces.

From The Little Engine That Could to The Polar Express, trains have always had a mythic hold on boys' imaginations. Why some people get hooked for life is a mystery, but Jon Berson, author of the 1997 suspense novel Foamers, has a theory. "Just like there's an oral stage, there's a train stage," he says. Railfans simply get fixated during the latter. Some memorize commuter schedules; others photograph cabooses. Like idiots savants, they exhibit an almost encyclopedic knowledge of operating procedures. Their thirst for ephemera, combined with a zeal for eyeballing trains up close, has made for uneasy relations with the people who run the lines, particularly in the wake of the 9/11 attacks and the 2004 bombings of commuter stations in Madrid. One railfan in Texas spotted taking notes beside the tracks in 2002 was pulled from his truck and grilled by police and FBI agents for five hours.

Three years ago, officials at BNSF deputized foamers to help the railroad spot suspicious activity. But engineers still fear them, citing instances in which zealots have stood on the tracks or climbed signal boxes to take pictures. To the engineers, the Chatsworth crash was a grim reminder of the potential for peril along the rails. The train Sanchez was driving knifed through an iron switch at 42 mph, flattening it like "a banana," according to the NTSB. The force of the collision drove the Metrolink engine back into the first passenger car, slicing bodies in half and encasing them in ribbons of steel. Rescue workers had to be rotated in shifts to minimize the toll of the horrors they witnessed.

In Glendale, California, in 2005, 11 Metrolink passengers died when their train collided with a gasoline-soaked Jeep Cherokee left on the tracks in a botched suicide attempt. The news from Chatsworth was even more chilling. "If anything good is to come out of this awful week," read one post on a website frequented by engineers, "I hope it's the complete eradication of foamers from railroad property." "Fucken [sic] train buffs and there [sic] stupid obsession," read another on YouTube. When a story surfaced six weeks later about a 17-year-old foamer who'd posted images from his joyride in the cab of a Chicago commuter line on MySpace, the animosity reached full boil.

So it's surprising to see how much latitude the track officials grant the railfans in Fullerton. "I think they feel it's better that we're in one place than spread out on the line where they can't see us," says Brett Canedy, a man in a green Hollister sweatshirt and a 30 Rock ball cap. At 29, he's something of a rookie among Fullerton's middle-aged foamers, but his social confidence and knowledge of rail operations lend him a certain king-of-the-nerds authority. "Watching trains makes you feel connected to the world," he muses as a freight carrying shipping containers from China rumbles by, rattling the leaves on the palms. Canedy works for the department of public works in Mission Viejo. He's been a Fullerton regular for five years. The moment you begin to wonder why such a good-looking, intelligent man would spend his Saturday nights watching trains, he says, "Some people go to bars. We hang out at the train station. It's a real community."